1. Field of the Invention
The invention relates to an apparatus and method for controlling an internal combustion engine that includes a variable valve mechanism that can change at least one of the maximum lift amount and the working angle of an intake valve.
2. Description of the Related Art
Valve lift control systems are proposed, which control the maximum lift amount and the working angle of a valve of an internal combustion engine according to the operating state of the engine. Japanese Patent Application Publication No. JP-A-2001-263015 describes a typical valve lift control system. In an internal combustion engine using such a variable valve lift control system, the amount of air taken into a combustion chamber can be reduced by reducing the maximum lift amount and the working angle of an intake valve. Thus, when the amount of air required for combustion is small, for example, during idling operation, the amount of air taken into the combustion chamber can be reduced by reducing the maximum lift amount and the working angle of the intake valve. In the case where the amount of air taken into the combustion chamber is reduced by reducing the maximum lift amount and the working angle of the intake valve, pumping loss can be reduced as compared to the case where the amount of air taken into the combustion chamber is reduced by reducing the opening amount of a throttle valve. That is, loss of output of the internal combustion engine can be suppressed, which improves fuel efficiency.
Thus, by reducing the pumping loss, fuel efficiency is improved. However, this reduces the rotational resistance against the idle rotation of the output shaft after fuel injection and ignition are stopped to stop the engine. This results in the increase in the time required to completely stop the internal combustion engine.